Valve for pneumatic tools



March 13, 1928.

H. JESCHKE VALVE FOR PNUMATIG TOOLS Filed NOV. 6. 1926 Inventor l by .d-orlwy Patented Mar. 13, 1928.

UNITED STATES PATENT OFFICE. f

HERBERT JESCHKE, OF DUISBURG, GERMANY, ASSIGNOR T0 DEMAG AKTIENGESELL- SCHAFT, OF DUISBURG, GERMANY.

VALVE FOR PNEUMATIC TOOLS.

Application led November 6, 1926, Serial` No. 146,733, and in German-y September 15, 1925.

The valves hitherto employed for controlling pneumatic tools, and which `have been designed for the economical use of compressed air, have the disadvantage that either the 'valve is highly complicated or, if it is not complicated, the striking piston that controls the valve loses its simple form and becomes comparatively weighty, whereby the speed of striking is reduced while the tool is increased in weight. In the mass production of pneumatic tools, however, it is of the greatest importance that-the tools shall be produced as simply as possible without, however, affecting the efiiciency of the joints between the respective moving parts. In valves that are designed for the economical use of compressed air several differential surfaces are necessary, and consequently several tightly fitting peripheral surfaces of different diameters. Experience has, however, demonstrated that it is almost impossible to secure an eilicient joint between these different peripheral surfaces, more particularly as it is generally necessary that parts of the tool may be replaced without tting. The faulty fitting between these complicated valve parts results in an increase in the consumption of compressed air, while at the same time the output of the tool is reduced. In contra-distinction to these valves, valves are also known, in which the peripheral surfaces to be fitted are of the same dialneter.

It has before been proposed to provide a valve for a pneumatic tool, which valve is moved in one direction by ther pressure of air compressed in front of the returning piston and is moved' in the other direction by means of a spring bearing against one end face of the valve when the pressure upon the opposite end face of the valve is neutralized by the opening of a passage by the piston on the percussion stroke, whereby communication between the space in front of the latter end'face of the valve and an annular recess in the valve forming an opposed difi'erential surface is established.

According to the invention in a pneumatic tool having a slide valve moved in one direction by a spring and reversed when the piston is making its return stroke by air compressed in front of the piston, the reversal of the valve during the percussion stroke is effected solely by the pressure of the spring upon one end face of the valve,

for which purpose the opposite end faces of the valve are of substantially the samearea and communication.between the space be tween the valveand the piston and the space in front of the end face of the valve against which the 'spring bears is established'by the piston during the percussion stroke.

The valve can be used for all kinds of pneumatic tools. In order to warrant a positive starting of the hammers, it is advisable either to connect a. space, which is continuously lunder the pressure of fresh air, or a space, which during the return stroke stands under fresh air, (e. g. valve shell) by a small bore with the rear cylinder space.

ln drills that reverse automatically this auxiliary connection has still greater importance, vin that frequently when the boring tool becomes held 'in the borehole, the. piston does notl make its normal return stroke, and the compression in the cylinder space behind the piston is not brought to a suiicicntly high point to ensure reversal. Thus there is the danger that the piston will cease to operate. If, however, compressed air entersI the cylinder space behind the pis- 'ton through the auxiliary passage above referred to, the pressure yincreases ink a very short space of time to such degree that reversal is effected and the percussion stroke is commenced. i Y

Two constructions fof the apparatus according to the invention are diagrammatically illustrated by way of example in longitudinal section in the accompanying drawing. K

Figure l illustrates the use of the valve according tothe invention in a pneumatic4 tool such as a pick at the commencement of the return stroke;

Figure 2 shows thehammer at the commencement of the percussion stroke of the piston;

Figure 3 shows how a percussion boring tool can be provided with the valve according to the invention. v

lVith reference to Fig. l, compressed air passes through the passage a into the annular passage Z), through the holes c, the annular recess (l in the valve body Z, through the passage e and thus below the'percussion piston whereby the latter is driven upwards. In the n'ieanwhile the cylinder space abovek the `piston has commenced to discharge its air through the exhausty passages y, then through the valve passage /i and the conipression passage through the space above the valve, with which said latter' passages coinrnunieate into the exhaust passages and g. vWhen in the return movement ot the piston the upper edge ol the piston covers the compression passage il, the air in the space above the piston is conilpiressed and l'orccs the slide valve Z upwardly against the valve springs o. At thc same time the space below the piston is emptied of air through the exhaust passages y. The piston f is brought, to a standstill and reverses its direction ot movement. ln the percussion stroke (Figure compressed air passes from the passage u through the annular passage L and the holes la to a position above the piston f and drives it, downwardly. The air below the piston, after the latter passes the cX- haast port g esfapes through the passage e. the annular passage (l in the valve shell l. the port p and the exhaust passages i and g.

lhen the upper edge of the piston f uncovers the passage l1, the lspace above the piston is in connnunication with the space above the valve, Z and the two spaces are then under equal pressure: the valve spring o is then ahle to press the slide valve 7 downwardly and thus produce its return stroltc. when thc percrssion piston strikes the tool the air at'. the rear ot the piston escapes through the exhaust passages (r/ and the c vcle of operations is repeated.

rPhe valve on the drillingl tool illustrated in Figure 3 operated in similar manner. The rel'ercncc letters shown in this drawing correspond to those used in Figures l and Q, the auxiliar)v passage hcreinbel'ore described being represented bv the reti-rence letter r. This auxiliary passage r connects the inletY passage a tor the compressed air with the slide valve cylinder space s and the air front passage i' enters this space and also through passageiva)v ne, into the space t in the working c vlinder at the rear oit pis ton f. The air drives the valve Z to the right against the action of the spring 0 and the valve ents ntl communication between the inlet u and the passageway leading to the 'l'ront end oi' the. cylinder. When the piston moves outwardly compressed air from the space t flows through passageway /t to the right of the valve l. and thc pressuresv are thus ctpialized on hot h sides of the valve. andy the spring reverses the slide valve. The air aty the r an' of the piston f then exhausts through passageway g. and compressed air entersl the front. end ol the. c vlindcr through passageway c and returnal the piston. l l' the boring tool becomes lixcd in the bore hole. as, heretofore referred truand does not complete its return stroke. compressed air con tinuouslv passes through passagewatv r and etl'ects reversal ot' valvc l and ol' the piston and the latter operates out with a shorter stroke.

l claim:

In a percussive tool the combination of a cylinder, a valve chest having communication with opposite ends of said c vlindcr and having a port adjacent one end communieating with a source of operating fluid and an exhaust; port communicating with the op posite end. a c vlindrical valve. slidablv mounted in said valve chest and adapted to control communication between .said .souri-c ot compressed tluid and opposite ends oll said cylinder, a springr tmcrativelv engaging one side ol' said 'alve and serving to normall)v hold said valve in position to close conununication to one end ol' said c vlinder. ."aid cylinder having a piston controlled relielI port and a piston controlled pressure eipializing port cach normallvl coniinunicating with said valve chest on the spring prt .sed side o1" said valve. wher-eb) fluid pressure is etpialized on opposite sides of said valve during the major portion oll the travel of said piston toward the cnil ol said evlinder norrnallv closed b v said valve under the action ot' said spring. until said pressure. equalizing port is covered h v said piston7 permitting snliicient iluid pressure to be built up under said valve to 'anse said valve to move in said valve chest to reverse the direct-ion of flow of said operatingr fluid.

HERBERT .'lllSCHlli). 

